A detailed gravity survey (Isherwood, 1975) was undertaken as a follow-up to a regional gravity survey of the area in order to detail a low in the Clear Lake volcanics. The low (Fig. 5 ) was thought to be caused by an intrusion of molten rock which would be mass deficient. Modeling and interpretation indicated a+K139
chamber-like feature with a radius of approximately 7 km within 7-8 km of the surface.